Why are Association football and American football both called football?

When a foot comes in contact with a ball, the game gets to be called football.

In Australia there are four different football codes - Australian football, usually called "footie" or "AFL" after the premier competition in the code; Rugby Union football, usually called "Union"; Rugby League football, usually called "League"; and Association football, which is always called soccer. American football is known as Gridiron. Gaelic football is also known here and an international series is played between Ireland and Australia using a compromise set of rules mixing Australian and Gaelic football.

In the rest of the world, "football" is what the Americans call "soccer".

What the Americans call "football" is called "American football" or something similar (the French equivalent is "American rugby").

The reasons for this date back decades, but soccer never took hold in the US, whereas it became enormously popular elsewhere - particularly in Europe and Latin America.

The US has been much more interested in soccer for the past 20 years - continued appearances in the World Cup has helped increase its popularity - but football is now so well established as the No. 1 sport in the US, it willl always have the priority where the word "football" is concerned.

"Soccer" - Association Football - has become by far the most dominant form of football across the world, such that only in the USA do you have to say "soccer". In the rest of the world "football" in a news headline or on TV is Association Football. When anybody says "The Football World Cup, or even possibly just "The World Cup", they mean soccer.

There are several other forms of "football" across the world, e.g. "Australian Rules", "Rugby League", Rugby League", nearly always referred to by those defining names, in order to separate them from "Football", meaning soccer. In most of the world "American Football" is called thus, meaning the game that looks a bit like rugger (Rugby Football), in which there is much handling of the ball, and not much kicking by foot.

Same as Rugby Football - it describes a game which involves (some) kicking of a ball.